In various machining operations a tool, for instance a cutting bit, is held offset from an axis and is orbited about this axis as it engages and cuts or grinds a stationary workpiece. It is also common in some operations for the tool to be moved radially of the axis as it is orbited, for instance to plane the surface of the workpiece, cut a circular groove in the workpiece, cut a hole centered on the axis in the workpiece, or even turn an inside surface of a hollow workpiece.
To this end the holder normally has a main body that is rotated about the axis and that carries a slide displaceable diametrally of the axis and in turn provided with a seat that the tool is mounted in. A motor on the main body is capable of displacing the slide as needed by the machining operation, being connected through an appropriate linkage to the slide.
German 1,193,768 issued May 26, 1965 to Mottu describes a boring head in particular for a coordinate-type boring machine that has a bore-head housing with a holder for securing to the spindle and a slide movable radially of the spindle axis and adapted to hold a bit. In order to set the radial position of the slide there is a servo drive that is mounted in the boring head and that is digitally controlled via a sensor arrangement. The motor and the sensor of the servo drive are diametrally opposite one another in the bore-head housing.
Electricity is fed via commutator rings to the motor that shifts the slide in the bore head. The slide, which is guided on rollers, is displaced by a micrometer-type screw with each end of the screw carrying a gear forming part of a drive between the motor and the micrometer screw. The commutator rings are subject to fouling in use and can open-circuit the motor, in particular when the machining process uses cutting oil. In addition the gear-type drive does not accurately move the tool, and when the tool is moved relatively far out the center of mass of the bore head is offcenter, causing it to vibrate when rotated.
Thus U.S. Pat. No. 3,710,659 of Pagella describes an automatically controlled tool-holding device that is also adapted to be mounted on a rotating drive spindle. It has an electric drive motor that is fixed in the tool head and whose output shaft extends on the rotation axis of the device, making the unit fairly long. A worm gear on the output shaft engages with a helically threaded shaft that shifts the slide radially. Such a system also does not displace the slide highly accurately and creates an offcenter mass when the slide is shifted widely. Once again, the motor is supplied power through commutator rings subject to fouling.
In German 3,526,712 issued Jan. 29, 1987 a planing or outside turning system is shown having a transversely displaceable slide that holds the cutting tools. Once again a drive motor and a position detector are provided in the head and are connected through a complex commutator system with the control and power lines. The transversely aligned drive motor engages via a drive in a gear that meshes with a rack that itself moves the slide. The position detector is a glass rod and a housing mounted feeler which create an extremely sensitive and failure-prone assembly. Furthermore the device is difficult to install and is subject to frequent breakdowns.
German patent 5,330,822 issued Mar. 16, 1985 to Schneider describes a tool head with a base body, a tool shaft projecting axially from the base body and couplable with the machine drive spindle, and at least one transversely displaceable and axially projecting slide. A position-sensing system is provided in the rotary head. The base body holds and electrical servomotor whose generally cylindrical body extends perpendicular to the head rotation axis. Power is transmitted inductively to the motor and the position information is transmitted via infrared to the controller. As a result of the construction, only a very short radial stroke is possible for the slide.
German 197 17 172 issued Nov. 6, 1997 to Scheer has an axially centered motor whose output shaft extends forward and carries a gear that meshes with a rack on the slide. While the axial centering does keep the system fairly well centered on the axis to reduce vibration, it makes the device rather long and bulky.
The device of German 41 37 364 issued May 21, 1992 to Mukai has several motors rotatable about perpendicular axes for controlling a multispindle lathe. This system is fairly complex and not readily adaptable to a chuck or tool holder where the tool is moved radially of a rotating body carrying it.